A ball bearing is known in the prior art as a type of rolling-element bearing that uses balls to maintain a separation between bearing races. Such a prior art ball bearing 100 is shown in FIG. 1 in side view wherein the balls 102 are entrained between an outer bearing race 101 and an inner bearing race 103. Another example of a prior art ball bearing shown in perspective view cross-section in FIG. 2 is illustrated at 104 having an outer bearing race 105, a notch 108 in the outer bearing race, a retainer element 106, and balls 107. Instead of balls, rollers may be used entrained between bearing races.
Bushing bearings are also known such as shown at 109 in perspective in prior art FIG. 3, and are shaped as a cylinder for receiving a shaft. Such bushing bearings for example oil impregnated bushing bearings, are very inexpensive alternatives to ball and roller bearings such as shown in FIGS. 1 and 2. However, because of the relative sliding motion between the bearing bushing and a shaft passing through the bearing bushing, bushing bearings wear at a faster rate than the rolling motion in ball and roller bearings. Furthermore, as bushing bearings wear, the initial small diametral clearance between the bushing bearing and the shaft increases. The increased clearance can result in increased noise such as a “slapping” noise when the bushing bearing is used in a reciprocating mechanism. At a critical increase in diametral clearance, the circumferential lubrication boundary layer between the ID of the bushing bearing and the OD of the shaft will locally break down, resulting in bearing failure. Such a bearing failure will not only damage the bearing but will also damage the shaft. Ball, roller, and bushing bearings are also susceptible to failure if exposed to dirt or water if a seal is not used or if the seal fails.
The main drawback of the ball or roller bearing is that they are much more expensive than bushing bearings and are very susceptible to contamination, such as dirt or water. With respect to conventional bushing bearings, as they wear, not only is there increased noise due to “slapping” of the shaft against the bearing, especially in a reciprocating motion application, but there is no way of easily determining if a critical clearance has been obtained where the bearing will begin to fail, damaging both the bearing and the shaft.